This invention relates to a heat-sensitive recording head having a drive means which drives a plurality of heat generating elements on a heat-sensitive recording head simultaneously, or in plural groups, according to the number of picture elements to be printed for one line.
In a heat-sensitive recording device with a heat-sensitive recording head, video signals are successively stored in the heat-sensitive recording head itself, or in a shift register provided separately, and data are recorded by causing the heat-generating elements on the heat-sensitive recording head to generate heat according to the video signals thus stored.
FIG. 1 shows the arrangement of a conventional heat-sensitive recording device of this type. A received signal 1 transmitted through a transmission path is written in a buffer memory 2 which stores the video signals of each line. A sequencer 3 operates to control the operation of the heat-sensitive recording device. More specifically, the sequencer 3 applies a reading control signal 4 to the buffer memory 2 with predetermined timing, so that a video signal 5 is read out of the buffer memory 2. The video signal 5 is applied to a shift register 6 which stores the video signals of one line. That is, the video signals 5 are read out of the buffer memory 2 in response to the control signals 4 and are successively applied to the shift register 6. At the same time, the sequencer 3 applies a drive control signal 8 to a block drive system 7 to control the latter.
The shift register 6 is a circuit element for converting a series signal into a parallel signal. Lead wires 9 connected to the output of the shift register 6 are divided into a plurality of blocks (or groups) which are connected to the input terminals of switching circuits 11.sub.1 through 11.sub.n (n being an integer). These switching circuits 11.sub.1 through 11.sub.n are connected to a common power source 12. In response to timing pulses 13.sub.1 through 13.sub.n from the block drive system 7, voltages corresponding to the video signals are applied to lead wires 14 which are connected to switch output terminals. The other end of the lead wires 14 are connected to the first ends of heat generating elements 16 arranged on a heat-sensitive recording head 15, respectively, and the second ends of the heat generating elements 16 are grounded. The heat generating elements, to which the voltage is applied because of the presence of a video signal to be printed, generate heat. On the other hand, the heat generating elements, to which no voltage is applied because of the absence of a video signal to be printed, generate no heat, being maintained at the earth potential. Accordingly, as a heat-sensitive recording sheet is run in a direction perpendicular to the line of the heat generating elements 16, video data are recorded thereon by the selective heat generation of the heat generating elements 16.
In the conventional heat-sensitive recording device described above, the recording operation of one line is divided into a plurality of recording operations with the aid of the block drive system 7, in order to limit the maximum number of heat generating elements operated at a time, thereby to reduce the maximum power consumption and to set the dimension and cost of the power source 12 within predetermined ranges. However, in recording an ordinary original, the area which includes no data to be printed (hereinafter referred to as the background area, when applicable) is much larger than the area which includes data to be printed, and the device described above suffers from a drawback in that the power capacity is not economically used. Furthermore, as the recording operation of each line is divided into a plurality of recording operations as was described above, it is difficult to increase the recording speed.
FIG. 2 shows the arrangement of a heat-sensitive recording device which has been proposed to solve the above-described problems. In FIG. 2, those components which have been described with reference to FIG. 1 are therefore similarly numbered. In the device, the video signal 5 of one line from the buffer memory 2 is applied to the shift register 6 and to a counter 18 simultaneously. The counter 8 counts a video signal (a black video signal) which is included in the video signal of one line and is to be printed. Upon completion of the counting operation, the counter 18 applies a division specifying signal 19 to a sequencer 21 in correspondense to the count value. Thereupon, the sequencer 21 changes the drive control signal 8, to specify the number of recording operations which the block drive system is to carry out in recording one line. For instance in the case where the ratio of black video signals to be printed to the number of video signals of one line is less than 1/4, the sequencer 21 causes the block drive system 7 to output all the timing pulses 13.sub.1 through 13.sub.n at the same time, so that one line is recorded simultaneously, i.e., in one recording operation. In the case where the proportion of black video signals is larger than 1/4 (inclusive) and smaller than 1/2, the sequencer 21 causes the block drive system 7 to firstly output some of the timing pulses 13.sub.1 through 13.sub.n and then the remaining number, so that one line is recorded by two recording operations. In the case where the proportion is larger than 1/2 (inclusive), the block drive system 7 outputs the timing pulses 13.sub.1 through 13.sub.n in four groups, so that one line is recorded by four printing operations.
However, in this proposed heat-sensitive recording device, the recording division number cannot be discriminated until the video signals of one line have been completely counted and set in the shift register 6. Therefore, the transmission of a busy signal for temporarily suspending the video signal transmission is delayed. Accordingly, the buffer memory 2 must have a larger capacity than is conventional. This is a problem involved in the conventional heat-sensitive recording device.
Furthermore, in the conventional heat-sensitive recording device, the recording division number varies for every line, and accordingly the recording time varies for every line. Accordingly, after the recording division number has been discriminated, a drive pulse for moving the heat-sensitive recording sheet to the next auxiliary scanning position is applied to the sheet feeding motor. Therefore, even in the case where a line can be recorded by a single recording operation, a method cannot be employed in which, before the recording operation starts, the drive pulse is produced with the response time of the sheet feeding motor taken into account. Thus, the recording speed cannot be sufficiently increased.